Senin, 21 Oktober 2013

Are Insomnia's Effects on the Brain as Bad As They Feel?

Insomniacs don't just suffer at night. During the day, they often feel sleepy, have trouble concentrating and report greater difficulty with work or school performance than individuals who get adequate sleep. But researchers are intrigued by an apparent discrepancy: Despite what insomnia patients experience subjectively, they often seem able to perform cognitive tasks as well as people getting adequate sleep. One possibility is that insomnia doesn't lead to inferior performance after all—maybe it just feels that way.

Using brain imaging technology, researchers monitored 25 people with insomnia and 25 normal sleepers as they performed an eight-minute working-memory task involving the processing and storing of short-term memory. The subjects underwent functional magnetic resonance imaging scans while viewing a series of letters on a screen, one at a time, and identifying which were repeats of letters displayed earlier in the sequence.

As the exercises became more difficult, the normal sleepers had increased activity in parts of the brain such as the dorsolateral prefrontal cortex while the insomnia subjects didn't. And the poor sleepers couldn't turn off the brain's "mind wandering" regions, also known as the "default mode" network, located generally along the brain's midline. These regions are ordinarily active when a person isn't engaged in goal-directed behavior and they are suppressed when the person switches to a task.

Despite the differences in their brain activity, the two groups performed the memory task equally well, said Sean P.A. Drummond, an associate psychiatry professor at the University of California, San Diego, and a sleep researcher at the VA San Diego Healthcare System, who is the study's lead author. The study was published in the September issue of the journal Sleep.

"They're doing the task just fine but their subjective sense is sort of like they're running through mud," said Dr. Drummond. "It's just so much harder to do."

The more the insomnia patients subjectively reported sleepiness and difficulty concentrating, and the worse they subjectively reported performing their task, the greater was their inability to turn off the default-mode regions, as measured by the MRI. "There's no doubt that what's going on in the brain could be measured as less efficient," Dr. Drummond said.

"For the good healthy sleepers, the harder the task becomes the more they recruited the working memory parts of the brain," he added. "The insomnia patients, in contrast, weren't able to ramp up these parts of the brain the way they should have." The subjects with insomnia had primary insomnia, meaning their difficulties falling asleep or staying asleep weren't related to a health condition, such as sleep apnea.

More research is needed to understand how insomnia patients were able to compensate and perform the tasks equally well despite the apparent dysfunction in brain activity. The ultimate goal of this kind of research is to determine the environmental and genetic causes of insomnia and develop novel treatments.

Some 10% to 15% of U.S. adults suffer from insomnia, particularly middle-aged and older adults, women and those with medical or mental health problems, said Nathaniel Watson, co-director of the University of Washington Medicine Sleep Program, in Seattle. The UC study is a "physiological explanation of why [individuals with insomnia] may have trouble in their day-to-day functioning," he said.

Laura Newmark, a 36-year-old in New York City, said she has had difficulty sleeping for six or seven years and feels it many days. "It is hard at work because there are so many details and I have trouble keeping track," said Ms. Newmark, who handles public relations for an artists' market. "I feel like it definitely impacts my ability to be fully present."

Marjohn Heath, a 43-year-old office manager, said she has suffered from insomnia for more than 15 years and she feels her mind wandering after a poor night's sleep.

On a recent Friday at her job at a Bethesda, Md., energy efficiency solutions company, her boss handed her a stack of journals and asked her to photocopy only the ones with Post-its. "I copied all of them," she said. "I read the note and it totally didn't register. I read it with my eyes…but I didn't process it."

"I have to make a significant effort sometimes not to let my mind wander or float away or get involved in things that are distracting," she said.

Daniel Buysse, a professor of psychiatry at the University of Pittsburgh School of Medicine, said he has done studies in people with insomnia that look at regional brain glucose metabolism during sleep and wakefulness using positron emission tomography (PET). The nuclear medical-imaging technique enables researchers to look at which areas of the brain are more or less metabolically active, he said.

The scans have shown that individuals with insomnia, even when asleep, have more activity in the arousal centers in the brain as compared with good sleepers. Ongoing research also has found that during sleep, those with insomnia have more activity in brain centers associated with mind-wandering activity.

"I kind of wonder whether that may be a neurosignature of the experience of insomnia, where people say, 'I feel like I wasn't asleep all night,' " Dr. Buysse said. The ultimate goal, he said, is to see how treatment affects the brain activity.

"If there are particular regions in the brain that are more active in people with insomnia when they're asleep, we might think of other techniques" for treatment, he said. For example, transcranial magnetic stimulation, a method of treating disorders such as depression and anxiety, can change activity in specific brain regions.